1. Technical Field
The present invention relates to a method for driving a discharge lamp having a pair of electrodes, a driving device, and a projector including a light source incorporated with such a discharge lamp.
2. Related Art
Heretofore, a lighting method for a high-intensity discharge lamp using a single driving waveform is known. If lighting by a single driving waveform continues for a long time, the electrodes continuously have a predetermined temperature distribution for a long time, and as a result, asymmetry of the electrodes caused by a time-variant state change tends to increase as time passes. For this reason, a plurality of concavo-convexes are generated around the tip portions of the electrodes, and flicker occurs. In order to solve this problem, a lighting method for a high-intensity discharge lamp is known in which the absolute value of an AC lamp current to be supplied to the high-intensity discharge lamp is set constant, and the AC lamp current is pulse-width modulated (JP-T-2004-525496). Specifically, the ratio of a pulse width of a positive pulse and a pulse width of a negative pulse is pulse-width modulated with a frequency lower than the lighting frequency.
However, as described in JP-T-2004-525496, when the AC lamp current is pulse-width modulated, for example, if a light source is provided with an auxiliary mirror in order to efficiently converge light to be emitted forward, an electrode on the auxiliary mirror side may be excessively deteriorated, and a pair of electrodes may be deteriorated unevenly.